1. Field of the Invention
The present invention relates to a magnetic sensor switch that is operable in response to external magnetism to turn its contacts on and off, and more particularly, to an elongated and miniaturized magnetic sensor switch of the type that comprises a magnetic sensor responsive to approach of a magnet, electrical contacts, and a movable contact piece adapted to be operable in accordance with the movement of the magnetic sensor to turn the electrical contacts on and off.
2. Description of the Related Art
As is disclosed in Japanese Patent Application Public Disclosure No. hei 6-347559 (347559/1994), for example, a magnetic sensor consisting of a combination of a permanent magnet and a reed switch responsive to magnetism has been heretofore known. As shown in FIG. 1, the magnetic sensor disclosed in the Japanese Patent Application Public Disclosure No. 347559/1994 comprises an elongated cylindrical case 71 made of a non-magnetic material, a reed switch 75 disposed in the interior of the case 71 generally in the center thereof, a columnar permanent magnet 73 mounted in the interior of the case 71 at the forward end (left-hand end as viewed in the drawing), a magnetic plate 87 attached to the outer side wall of the enclosure (glass tube in this example) 77 of the reed switch 75, and a magnetism adjusting permanent magnet 74 mounted at the peripheral area of the glass tube 77 adjacent one end thereof. The two permanent magnets 73 and 74 positioned on the opposite sides of the reed switch 75 are configured such that the opposing sides of the magnets 73 and 74 have the same magnetic polarity. In this example, the magnetic polarities of the opposing sides (the reed switch side) of the two magnets 73 and 74 are set both to be the S magnetic pole.
The reed switch 75 is positioned generally in the center of the case 71 by two spaced rings 76 and 78 both of which are made of heat-resistant, electrical insulating material. The root portion of the case 71 is mounted to a sensor mounting base 95 by means of a bushing 91 made of rubber. Lead wires 96 and 99 leading out from reeds 93 and 94, both being made of a magnetic material, of the reed switch 75 are connected to suitable heat-resistant, insulated wires 89 and 90, respectively, that extend to the outside through the root portion of the case 71. As is well known, the forward ends of these reeds 93 and 94 comprise contact portions 79 acting as electrical contacts.
Next, the operation of the magnetic sensor constructed as described above will be briefly explained with reference to FIGS. 2 and 3. FIG. 2 shows magnetic lines of force generated from the magnetic sensor shown in FIG. 1 when the magnetic sensor is in the standby state in which there is no magnetic substance (object) or magnet in the vicinity around the sensor. From FIG. 2, it will be appreciated that there is a very weak magnetic field produced in the vicinity of the contact portions 79 of the reed switch 75. The distribution of the magnetic lines of force generated from the magnetic sensor during this standby state may be preliminarily adjusted by moving the magnetism adjusting permanent magnet 74 longitudinally of the case 71. When the magnetic field applied in the vicinity of the contact portions 79 of the reed switch 75 is relatively weak as shown in FIG. 2, the contact portions 79 remain open, and hence the reed switch 75 is in the off state.
As a magnetic substance or magnet approaches the vicinity of the magnetic sensor in the standby state, the magnetic field applied to the reed switch 75 changes. FIG. 3 shows magnetic lines of force generated from the magnetic sensor when two iron balls 97 and 98 being magnetic material approach the vicinity of the forward end of the reed switch 75. As is apparent from FIG. 3, the magnetic field in the vicinity of the contact portions 79 of the reed switch 75 is significantly intensified as compared with that in the standby state. As a result, the reeds 93 and 94 made of a magnetic material magnetically attract and contact each other, and hence the contact portions 79 go to on state. Further, the detailed construction, structure and operation of this magnetic sensor are disclosed in Japanese Patent Application Public Disclosure No. 347559/1994. Accordingly, further description thereof is omitted for purposes of convenience.
This magnetic sensor includes the magnetic plate 87 disposed in the vicinity of the contact portions 79 and the magnetism adjusting permanent magnet 74 positioned at the one end of the reed switch 75 near the base of the case, in addition to the permanent magnet 73, so that the magnetic field produced by the permanent magnet 73 in the vicinity of the contact portions 79 of the reed switch 75 may be adjusted by the magnetic plate 87 and the magnetism adjusting permanent magnet 74 to control the dynamic or operating sensitivity of the contact portions 79 of the reed switch 75.
As discussed above, this magnetic sensor is configured such that the magnetic field produced mainly by the permanent magnet 73 is applied directly to the reed switch 75 and the contact portions 79 of the reed switch 75 is controlled to turn on and off by that the applied magnetic field is varied by a magnetic substance or a magnet approaching the magnetic sensor. Otherwise stated, this is a magnetic switch of the type in which the magnetic field applied directly to the reed switch 75 is varied by an approaching magnetic substance or magnet whereby the opposing reeds 93 and 94 of the reed switch 75 are attracted to each other so that the contact portions 79 are controlled to the on position.
It is thus to be understood that the switch of this magnetic sensor would not be turned on unless there occurs a change in the magnetic field to some extent. Further, this magnetic sensor will be turned on, irrespective of the polarity of a magnet approaching the magnetic sensor and even if the approaching object is a magnetic substance or object rather than a magnet. For this reason, the illustrated prior art magnetic sensor can not be used in applications where the switch of the magnetic sensor is required to be turned on and off only when it is approached by a particular magnetic pole of a magnet.
In addition, because the prior art magnetic sensor as described above utilizes a reed switch, it has the disadvantages that the cost of manufacture is correspondingly increased and moreover, in the event of failure of the contact portions, the entire reed switch must be replaced, which leads to an increase in the maintenance cost.
An object of the present invention is to provide an elongated and miniaturized magnetic sensor switch that does not utilize a switch such as a reed switch in which a magnetic field is applied directly to the contact portions thereof.
Another object of the present invention is to provide an elongated and miniaturized magnetic sensor switch in which a magnetic sensor thereof is responsive only when a particular magnetic pole of a magnet approaches it, to turn electrical contacts of the switch on and off through a movable contact piece thereof.
In order to accomplish the foregoing objects, in one aspect of the present invention, there is provided a magnetic sensor switch that comprises: an elongated magnetic sensor that has N magnetic pole at one end thereof and S magnetic pole at the other end thereof and that is mounted for rotation through a predetermined angle in the clockwise and counter-clockwise directions; a movable contact piece provided with a pair of contacts; a pair of fixed contact pieces located in opposition to the pair of contacts of the movable contact piece; a common contact piece electrically connected with the movable contact piece; and a member that is located at a predetermined position in a region outside of the rotating radius of the magnetic sensor and in the vicinity of the one magnetic pole of the magnetic sensor and that imparts a biasing force for holding the magnetic sensor at a position rotated through a predetermined angle.
The biasing force imparting member is an auxiliary magnet or a magnetic material that is disposed in a region outside of the rotating radius of the magnetic sensor and at a predetermined position on a longitudinal extension line of the magnetic sensor.
In one preferred embodiment, the magnetic sensor is an elongated generally cylindrical rod-like magnet having N magnetic pole at one end thereof and S magnetic pole at the other end thereof.
Alternatively, the magnetic sensor may be an elongated generally cylindrical member that comprises; a cylindrical central body made of a magnetic material; a first cylindrical magnet affixed to the cylindrical central body at one end thereof; and a second cylindrical magnet affixed to the cylindrical central body at the other end thereof.
The aforesaid magnetic sensor switch further includes a shaft securing member of a generally channel-shape in section that is fixed to the contact portion of the common contact piece, and the magnetic sensor is rotatably journalled by this shaft securing member.
The movable contact piece is attached to the magnetic sensor and to be rotated in union with the magnetic sensor when the magnetic sensor is rotated to bring one of the contacts of the movable contact piece into contact with the corresponding fixed contact piece.
The biasing force imparting member is an auxiliary magnet that is disposed in a region outside of the rotating radius of the magnetic sensor and at a predetermined position on a longitudinal extension line of the magnetic sensor, and the magnetic sensor is adapted to be held at a position rotated through a predetermined angle by an attractive force between the auxiliary magnet and the corresponding magnetic pole of the magnetic sensor, or by a repulsive force between the auxiliary magnet and the corresponding magnetic pole of the magnetic sensor.
The aforesaid magnetic sensor switch further includes a driving member that transmits the movement of the magnetic sensor to the movable contact piece, and this driving member is attached to the magnetic sensor and adapted to be rotated in union with the magnetic sensor when the magnetic sensor is rotated to transmit the movement of the magnetic sensor to the movable contact piece.
The pair of fixed contact pieces and the common contact piece are each strip-like members that extend in parallel from one end of an elongated generally rectangular substrate to the vicinity of the central portion between the longitudinal opposite ends thereof and that are mounted on the substrate, and the contact portion of the common contact piece is arranged generally in a row longitudinally of the substrate in a space between the contact portions of the pair of fixed contact pieces in such state that they are electrically insulated from one another.
In another preferred embodiment, the driving member is formed therethrough with a push-rod inserting hole in which a spring for imparting a biasing force and a push-rod are inserted in the order named, and the tip end the push-rod is in engagement with the movable contact piece.
It is preferable that the movable contact piece is constituted by a generally rectangular electrically conductive member, and a movable contact piece body of the conductive member is bent downwardly on the opposite sides of the longitudinal central portion of the conductive member to give slants extending downwardly toward the opposite longitudinal ends.
With the construction of the present invention described above, since a clicking action is added due to the provision of the auxiliary magnet or magnetic material, or a biased push-rod, the rotating movement of the magnetic sensor switch may be instantaneously effected and the switching-over of the switch may be instantaneously carried out. Consequently, the reliability of the switch may be enhanced. In addition, it is possible to reduce the cost of a product as well as the maintenance cost, because it does not utilize a switch in which a magnetic field is applied directly to the contact portions thereof such as a reed switch.